This invention relates to the field of computer systems. More particularly, a system and methods are provided for tracking responses to RDMA Read requests.
InfiniBand™ technology provides a flexible, scalable architecture for interconnecting servers, communication networks, storage components and other systems and devices. Computing and storage nodes have become distributed throughout many organizations' computing environments, and the InfiniBand architecture provides means for interconnecting those elements and others. For example, InfiniBand channel adapters can be used as bridges between an InfiniBand fabric and external communication systems or networks.
In the InfiniBand architecture, a queue pair (QP) defines an end-to-end connection between two nodes (e.g., servers, input/output components) at the transport protocol layer. A virtual lane (VL) operates at the link layer, and defines single-hop connections (e.g., between two switches, between a switch and a node). Each virtual lane has an associated service level indicating a quality of service to be afforded the traffic within that virtual lane. When an InfiniBand packet is communicated, it is communicated as part of a specific queue pair, which is assigned membership in a virtual lane for each hop. The virtual lanes used for different hops may vary, but the different virtual lanes may be associated with the same service level.
Queue pairs are flow-controlled by the receiving end of the end-to-end connection. Virtual lanes are flow-controlled by the receiving end of each hop. In particular, a node that receives traffic via an end-to-end connection or single hop may issue credits allowing the transmitting end (of the connection or hop) to send a specified amount of traffic.
A QP credit is generally issued for each message (e.g., one credit equals one message of up to 232 bytes), and each message may be segmented into one or more InfiniBand packets. For example, one message may correspond to one Ethernet packet to be encapsulated in one or more InfiniBand packets and passed to an external network. VL credits are generally in the form of blocks (e.g., sixty-four bytes per credit). When the receiving end of a QP or VL issues a credit, it is generally understood that an amount of storage space sufficient to store the corresponding amount of traffic will be available when the traffic is received. If storage space is not available, the QP at the receiving end may instruct the sender to retry the communication later. A VL reports a flow control error and then drops the packet.
The InfiniBand specification implies that each QP and each VL should be serviced at its receiving end by a separate FIFO (First-In, First-Out) queue. However, providing dedicated queues requires each queue pair and virtual lane to be provided with worst-case buffering to accept a maximum burst of traffic. This scheme results in an inefficient use of memory space because, at any given time, not every active QP or VL will even be configured, much less receiving enough traffic to require a full set of buffers, and therefore storage space dedicated to a particular (e.g., non-busy) QP or VL may be wasted. Thus, a need exists for a system and method for sharing buffers between multiple queue pairs or multiple virtual lanes, and/or between queue pairs and virtual lanes.
A shared storage space for virtual lane and queue pair traffic may allow more flexibility and scalability, but it would still be necessary to support flow control. For example, with shared storage space, the amount of storage used by each VL and QP should be tracked in order to calculate how many credits the receiving end can or should issue. Depending on whether any storage space is dedicated to a queue pair or virtual lane, or how much shared space is available for use by any queue pair or virtual lane, supporting flow control may become problematic. Thus, there is a need for a system and method for facilitating flow control in association with a memory configured for shared buffering of queue pairs and/or virtual lanes.
Further, at an interconnection between an InfiniBand fabric and an external system (e.g., an Ethernet network or other communication system), the use of discrete FIFO queues for each terminating QP (and/or VL) means that traffic to be transferred from a QP to the external system must be copied from its InfiniBand QP queue into a different queue or data structure for the external system (e.g., a network transmit module) before the traffic can be transmitted externally. This delays the transfer and causes additional inefficiency. Thus, there is a need for a system and method for avoiding inefficient memory operations when transferring communications between InfiniBand and an external system.
Also, if a single receive queue is used to store mixed types of traffic for a queue pair or other type of communication connection, a system and method are needed for interleaving the different types of traffic while avoiding the possibility of transferring traffic out of order. For example, a queue pair's traffic may include Send commands containing encapsulated outbound communications (e.g., Ethernet packets), Send commands containing RDMA Read descriptors (e.g., for retrieving outbound communications), responses to RDMA Reads, etc. Thus, different types of traffic should be handled without causing out of order processing of outbound communications.
A system and method are also needed to track responses to RDMA Read operations, so that a corresponding entry in a retry queue can be retired when all responses are received.